The invention relates to a method for the continuous hydrolizing of keratinaceous materials by heating under pressure for the duration of time it takes for the desired hydrolization to be achieved.
It is known to hydrolyze keratinaceous materials, especially feathers, bristle, nails, horn, hooves and the like, so that the keratinaceous material is converted into nutritious and digestible products, particularly for the feeding of animals.
From U.S. Pat. No. 3,617,313, a hydrolyzing apparatus is known whereby feathers are compressed to form a pressure-tight plug which is continuously introduced into the inlet of the hydrolizing vessel, thus closing the inlet in a pressure-tight manner. Water and steam are introduced into the hydrolizing vessel itself, while the vessel wall is a steam jacket for the heating of the product mass during the process, which is effected under vigorous agitation by means of paddle elements which contribute both towards the fluidization of the product mass and its transport through the vessel. The apparatus is both mechanically complicated and very energy-demanding, the reason being that the product mass must first be compressed to form a pressure-tight plug, and thereafter comminuted and fluidized in large amounts of water during the hydrolization.
Another apparatus for the continuous hydrolizing of keratinaceous materials is known from U.S. Pat. No. 4,286,884, whereby two vessels are used in the apparatus. In the first vessel, the material is heated and fluidized under such strong agitation that the material is comminuted. Hereafter, it is pumped by means of a special pressure-proof screw pump to a heated hydrolization reactor in which the hydrolizing takes place under suitable overpressure and temperature and under constant agitation, and from which the product mass is removed via a pressure-proof screw pump for further processing, especially the draining off of the very large amounts of water which are used to render the product capable of being pumped. This U.S.A. patent publication also provides a very detailed account of the chemical and biological aspects of the hydrolization, particularly with regard to the pressure and temperature conditions under which an optimum hydrolysis can be achieved. Therefore, this patent application does not touch upon these aspects in more detail, but refers to all that is known concerning these aspects from U.S. Pat. No. 4,286,884.
The object of the present invention is to provide an apparatus for the continuous hydrolyzing of keratinaceous materials whereby both the method and the apparatus are to a great extent simplified in relation to the prior art, so that a reduction is achieved in both the energy consumption and in the costs of the apparatus. Moreover, the necessity is avoided of having to add large amounts of water to the product mass, which must thereafter be removed from the hydrolyzed product.
In accordance with the apparatus of the present invention, the keratinaceous material is heated in a hydrolyzing vessel under pressure for a length of time it takes for the desired hydrolyzing to be achieved. The apparatus includes an elongated pressure-proof hydrolyzing vessel which, at its inlet end, is connected to an aluminum chute which is closed in a pressure-proof manner. The chute is arranged for the introduction of the material in batches and at intervals into the hydrolyzing vessel. The other end of the vessel is connected to a pressure-proof outlet chute arranged for emptying of batches of the hydrolyzed material. The hydrolyzing vessel includes means for direct injection of steam into the product mass, and the movement of the product mass through the vessel takes place in steps as plunger flow substantially in step with the inlet chute, and the pressure in the hydrolyzing vessel is greater at the inlet chute than at the outlet chute. The heating of the material is effected by the direct injection of steam, which at one and the same time heats, moistens and agitates the product mass. It is thus not necessary to use a hydrolyzing vessel where the vessel wall constitutes heating surfaces with pressure chambers for the heating medium. Since the product mass must be heated to a temperature in the range from approx. 130.degree. C. to approx. 200.degree. C., the heat jacket on the known kinds of apparatus must be heated to higher temperatures. Therefore, it is a great advantage to be able to avoid such heating surfaces, especially when seen from an operational and cost point of view.
Furthermore, all forms of agitators, pressure-proof shaft bushing with stuffing boxes etc. are avoided, which further reduces the cost of the apparatus and the operation hereof.
The hydrolyzation process itself is effected under overpressure at a temperature above 100.degree. C. In fact, the higher the pressure and the temperature, the more rapid the hydrolyzation. For example, if the pressure is approx. 8 bar, for which the corresponding temperature is approx. 175.degree. C., a hydrolyzation can be effected in approx. 15 minutes. If the pressure is increased to 10 bar, i.e. a process temperature of approx. 185.degree. C., the process time for the hydrolyzation is reduced to approx. 10 minutes.
The capacity of a given apparatus can thus be increased by raising the pressure and the temperature. Normally, a steam pressure in the order of 8 bar will be chosen, in that this will allow the use of ordinary industrial boilers.
The heating by the direct injection of steam results only in the moistening of the material, but the addition of the large amounts of water as with the known apparatus is avoided. The apparatus according to the invention can also use superheated steam, for example if the factory plant to which the hydrolyzation apparatus is to be connected is already using superheated steam. The amounts of water can be removed from the hydrolyzed product by pressing or drying before further processing, e.g. before being ground.
Driven by the difference in pressure across the vessel, the product mass moves by plunger flow through the vessel from the inlet chute to the outlet chute, in that a new part-portion is introduced regularly into the inlet chute and a hydrolyzed part-portion is ejected from the outlet chute. During operation with continuous hydrolyzing, the vessel is substantially filled with the product mass which, in relatively small steps, moves as plunger flow through the vessel. The throughput time is preferably in the order of 5-30 minutes, and it is worthy of note that this is when the raw material is introduced direct from, for example, the slaughtering plant, in that the raw material is fed to the inlet chute in an uncleaned and untreated condition. However, it will be possible to achieve lower processing times if the apparatus is arranged for higher process pressure and temperature. In certain cases, longer processing times will be able to be accepted, i.e. lower process pressure and temperature while still achieving a profitable production under the given conditions. Consequently, the method and the apparatus according to the invention have a very wide range of application.
In accordance with further features of the present invention, the hydrolyzing vessel is an elongated cylindrical vessel disposed in such a manner that the inlet end is above the outlet end, preferably so that the vessel is substantially vertical. By this arrangement, the plunger flow is assisted by gravity, and it will be possible to keep the apparatus in operation even with smaller amounts of material than those for which it is dimensioned, without this having any detrimental effect on the energy economy. By disposing the vessel in an upright manner, it is avoided that the product mass can adhere to the wall of the vessel and result in undesired packing together.
According to the present invention, the steam injection means are disposed in such a manner that the steam is injected through the vessel jacket in a direction substantially at right angles to the longitudinal axis of the vessel. With such an arrangement, is ensured that the product mass is agitated to a degree which is sufficient for the process to be effected as quickly as desired, i.e. in approx. 5-30 mins., see also above, and an advantageous energy economy is achieved. The number of injection pipes or valves and their distribution on the vessel jacket depends on several factors, among other things by the kind of material to be treated in the apparatus, i.e. on whether it is feathers, bristle, horn or nails, mixtures hereof or quite another material. In practice, the apparatus will be equipped with a sufficient number of steam injection nozzles which can be opened and closed as required. It will also be possible to use one or several central injection pipes for steam, e.g. disposed axially in the vessel, particularly in cases of vessels of large diameter.
In accordance with further features of the present invention, the inlet chute is configured as a pressure vessel with a closable connection to the hydrolyzing vessel, and a closable filling opening is arranged for a direct filling of the chute with raw materials plus the necessary steam pipes and valves. With such a construction, the resulting inlet chute for the hydrolyzing vessel is one which does not require any moving parts other than the closing devices used at the filling opening to the inlet chute and between the inlet chute and the hydrolyzing vessel. Among other things, the use of the known forced-feeding principle with a pressure-proof pump and all of the problems which arise in connection herewith is hereby avoided.
According to the present invention, the inlet chute further comprises at least one vacuum pipe with necessary valves for closing hereby enabling an underpressure to be established in the chute. With such an arrangement, the supply of air to the product mass is reduced, which increases the penetration of steam into the product mass, hereby achieving a quicker process for the reason that the product is heated more quickly.
The apparatus of the present invention further comprises a pressure-proof storage vessel for hydrolyzed material, with the vessel being connected to the outlet chute by way of a pipe. The storage vessel is held at a lower pressure than the outlet chute, and the storage vessel is connected to a pressure-free removal vessel through a shut-off valve. A steam pipe can be lead from the storage vessel to the inlet chute. With such an arrangement, the possibility is provided for the hydrolyzed product to be "shot" or by plunger flow conveyed from the hydrolyzing vessel to an economizer which is an intermediate storage vessel under lower pressure than the hydrolyzing vessel. The hydrolyzed product is hereby conveyed further without mechanical transport mechanisms or pumps. The introduction of limitations in the clearance in the transport path is hereby avoided, so that even relatively large pieces of material can pass unhindered all the way from the feed-in opening to the inlet chute to the pressure-free removal vessel. The only restriction on the transport is the opening in the closing valves, which in practice can be configured without problems with sufficient opening, the result being that it is not normally necessary to effect any kind of sorting of the raw material before it is introduced into the inlet chute.
The outlet chute system and the storage vessel can be coupled together with the inlet chute, hereby allowing the residual energy in the steam to be used for the preheating of the amount of material in the inlet chute, and possibly for the moistening hereof, whereby the energy utilization of the process is considerably improved. Moreover, this provides a substantially closed circuit for the steam, which to a great extent reduces the inconveniences arising from the smells from such a plant.
In accordance with the present invention, the product mass remains in the hydrolyzing vessel 5-30 minutes under a process pressure of 2-15 bar and a temperature corresponding hereto, whereby the process time remains short and the apparatus acquires a large continuous capacity.